When installing an oil production string, side pocket mandrels are frequently installed along the length of the string for enhanced recovery processes such as gaslift techniques. Each side pocket mandrel has a side pocket for receiving a gaslift valve. The gaslift valve is typically a one-way valve which allows higher pressure fluid in the annulus about the string to flow past the gaslift valve into the tubing string to assist in production.
Often, side pocket mandrels will be installed in the production string for future use, even though initially the well is self-producing. However, the production fluids often cause errosion of portions of the interior structure of the mandrel which causes leakage at the side mandrel between the tubing annulus and the tubing string. When such leakage occurs, it is necessary to plug the leak to maintain oil production.
Prior techniques for leak repair have frequently involved the use of separate upper and lower packers. Initially, a lower packer, often known as a "stove pipe packer", will be lowered into the tubing string to a position below the leak. The packer can then be set by wireline or a tubing string. If a tubing string is used, a drilling or workover rig must be positioned at the surface for operating the tubing string. Thereafter, a second, upper packer is run into the well, again on a wireline or by a tubing string to a position immediately above the leak. The upper packer will have a tailpipe extending downward from the upper packer which is stabbed into the lower packer to establish a sealed connection. The leak is thus isolated in the annular space between the interior of the side pocket mandrel and the exterior of the tailpipe between the upper and lower packers.
The present technique is quite expensive. If the packers are installed by tubing string, a drilling rig or workover rig must be set up over the well. If the packers are installed by wireline, it is very difficult to make the necessary sealed connection between the upper and lower packers to ensure an effective patch. A need therefore exists for a more economical and effective technique for patching such leakage in side pocket mandrels.